The present document is based on Japanese Priority Document JP 2000-203920, filed in the Japanese Patent Office on Jul. 5, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a cathode ray tube and a method for manufacturing thereof, and in particular to a technology preferably applicable to a cathode ray tube having on the inner surface side of a panel a conductive reflective film (metal back film) for enhancing the luminous intensity of the fluorescent material and a heat absorbing film for reducing the landing failure of the electron beam due to thermal expansion of a color selective mask.
2. Description of the Related Art
It is a general practice in a method of manufacturing cathode ray tube, in particular, in a method for manufacturing the panel therefor, that a fluorescent film is formed on an inner surface of the panel, and an aluminum conductive reflective film is then formed thereon. The fluorescent film is obtained by forming red, green and blue fluorescent material layers based on predetermined patterns at predetermined positions defined by a black matrix film (carbon film) patterned on the inner surface of the panel, the surface of which is then smoothened by an intermediate layer (filming layer) formed thereon. The conductive reflective film is obtained by vapor depositing an aluminum film by the vacuum vapor deposition process on the inner surface side of the panel already having such fluorescent film formed thereon. The fluorescent film 2 and the conductive reflective film 3 are thus formed on the inner surface side of the panel 1 as shown in FIG. 1.
In a general constitution of a color cathode ray tube, three electron beams emitted from electron beam guns are landed onto the fluorescent material layers of corresponding colors after being individually directed by a color selective mask (aperture grill, shadow mask, and the like). The color selective mask is then heated while being directly irradiated by the electron beams and is further heated by heat radiated therefrom and reflected by the conductive reflective film. This results in a considerable heat expansion of the color selective mask, which is causative of landing failure (positional deflection of the electron beams onto the fluorescent material layers) and undesirable color misalignment.
A known technique for reducing such landing failure of the electron beams is to form a heat absorbing film on the conductive reflective film on the inner surface side of the panel so as to absorb the radiation heat from the color selective mask, thereby suppressing the thermal expansion of such color selective mask.
In a conventional process, the heat absorbing film is formed after the conductive reflective film is formed by vapor-depositing aluminum onto the inner surface side of the panel. More specifically, known methods include spraying graphite dissolved in a solvent to the inner surface side of the panel having a conductive reflective film already formed thereon to thereby form a heat absorbing film; vapor-depositing aluminum under a low degree of vacuum to thereby form a heat absorbing film made of aluminum oxide (alumina); and vapor-depositing a blackening material other than aluminum (manganese, tin, and the like) to thereby form the heat absorbing film.
The conventional manufacturing methods as described above have however been disadvantageous in that requiring two separate film forming steps for forming conductive reflective film and the heat absorbing film on the inner surface side of the panel complicates the manufacturing process of a cathode ray tube (panel manufacturing process). In the case of using a single vacuum chamber for vacuum evaporation of the conductive reflective film and the heat absorbing film in order to simplify the manufacturing process undesirably, the film material composing the heat absorbing film diffuses on the surface of the conductive reflective film (metal diffusion), which may lower the luminous intensity of the fluorescent materials. Moreover, film formation by spray coating or the formation of aluminum oxide film at a low degree of vacuum has been suffering from a large lack of uniformity in the manufacturing, complicated management, and difficulty in obtaining heat absorbing film having stable characteristics.
According to the present invention, there is provided a method for manufacturing a cathode ray tube in which predetermined films are formed on an inner surface side of a panel having a fluorescent film formed thereon, comprising a first step for forming a conductive reflective film on the fluorescent film by depositing a first film material; a second step for forming a diffusion preventive film on the surface of the conductive reflective film formed on the fluorescent film; and a third step for forming a heat absorbing film on the diffusion preventive film formed on the conductive reflective film by depositing a second film material.
According to such method for manufacturing a cathode ray tube, in the process of forming the conductive reflective film using a first film material on the inner surface side of the panel and further forming thereon the heat absorbing film using a second film material, having the diffusion preventive film interposed therebetween, diffusion of such second film material on the conductive reflective film can successfully be prevented by the diffusion preventive film. This ensures desirable and stable characteristics and film qualities of the conductive reflective film and the heat absorbing film. In a cathode ray tube thus obtained, that is, in a cathode ray tube having on the inner surface side of the panel thereof a three-layered film comprising the conductive reflective film, the diffusion preventive film and the heat absorbing film, such diffusion preventive film allows the conductive reflective film and the heat absorbing film to fully exhibit their functions, which improves the display image quality.
In the case where the vacuum evaporation process is employed for the first and third steps in such method for manufacturing a cathode ray tube, the diffusion preventive film is obtained by oxidizing the surface of the conductive reflective film in a vacuum chamber used for the vacuum evaporation process after a degree of vacuum of the vacuum chamber is lowered at a predetermined level so that the conductive reflective film and the diffusion preventive film can be formed in the same vacuum chamber using a first film material only, and such diffusion preventive film can be formed by a simple process.
The conductive reflective film and the heat absorbing film can successively be formed within the same vacuum chamber by respectively supplying the first film material and the second film material to the separate heat sources, activating in the first step a heat source to which the first film material is supplied and activating in the third step another heat source to which the second film material is supplied.
According to the method for manufacturing a cathode ray tube of the present invention, the second film material composing the heat absorbing film will not diffuse on the conductive reflective film since the heat absorbing film is formed only after the diffusion preventive film is formed on the conductive reflective film after the formation thereof on the inner surface side of the panel. Such process can successfully form a conductive reflective film with excellent reflection characteristics (mirror effect) and a heat absorbing film with excellent heat absorption characteristics.